Bring a large pot of salted water to a boil. Cook macaroni until tender, about 8 minutes, then drain and rinse with cold water.

In a small bowl, whisk together mayonnaise, sour cream, cider vinegar, mustard, sugar, salt, and pepper until smooth.

Dice the celery, bell pepper, and scallions into small pieces.

In a large bowl, combine the cooled macaroni, diced vegetables, and relish. Pour the dressing over and fold gently until evenly coated.

Transfer to a serving bowl, cover, and refrigerate for at least 1 hour. Before serving, stir, sprinkle with paprika, and top with chopped hard-boiled eggs if using.